1. Field of the Invention
The present invention relates to a field emission type cathode, an electron emitting apparatus and a process for manufacturing the electron emitting apparatus.
2. Description of the Related Art
Various kinds of electron emitting apparatus having a field emission type cathode, e.g. plane type display device, i.e. panel type display device have been proposed. In order to display a bright picture, a cathode ray tube type structure in which an electron beam bombards a fluorescent screen to emit a light is generally adopted.
The plane type display device having this cathode ray tube type structure is such that, for example, as proposed in Patent Gazette of Laying-Open No. Hei 1-173555, a plurality of thermionic emission type cathodes, i.e. filaments are provided opposite to the fluorescent screen and the thermious produced by this cathode and the secondary electrons thereby are directed towards the fluorescent screen to cause the electron beam to excite the fluorescent screen of respective colours depending on a video signal for light emission. In this case, as the size of screen becomes large, such structure is adopted that the filaments are provided in common to a large number of pixels, namely, a large number of fluorescencer trio of red, green and blue forming the fluorescent screen.
Therefore, particularly with the large-sizing of the screen, the layout and construction of the filaments become complicated and besides, the filament itself becomes elongated.
Moreover, in order to make the size of plane type display device small, it has been practiced to make short of an electron gun or make large of a deflection angle of electron for aiming at shortening its depth. With the recent large-sizing of the plane type display device, the development of a thin structure of plane type display device is further desired.
On the other hand, in the conventional plane type display device, such a plane type display device is proposed that employs the field emission type cathode, the so-called cold cathode. An example of such plane type display device structure will be described below with reference to the drawings.
The plane type display device 100 shown in FIG. 1 is comprised of a body 102 of plane type white colour light emitting display device having a white colour light emitting fluorescent screen 101 and field emission type cathodes K arranged opposite thereto as well as a plane type colour shutter 103 arranged adjacent or opposite to the front face of the screen 101 on its arranged side.
As shown in FIG. 1, the display device body 102 is constructed in such a manner that a transparent front panel 104 and a rear panel 105 oppose to each other through a spacer (not shown) holding a predetermined space between both panels 104 and 105 and the peripherys thereof are sealed airtightly by the glass frit, etc. to form a flat space between the panels 104 and 105.
On the inner surface of the front panel 104 is formed the white colour light emitting screen 101 which is made by applying previously a white colour light emitting fluorescencer entirely, and its surface is coated with a metal-backed layer 106 of aluminum film, etc. as in the ordinary cathode ray tube.
On the other hand, on the inner surface of the rear panel 105 are arranged and mounted in parallel a great number of cathode electrodes 107 which, for example, extend vertically in the shape of belts.
These cathode electrodes 107 are covered with an insulation layer 108, on which gate electrodes 109 that extend, for example, in the horizontal direction nearly perpendicular to the extension direction of cathode electrodes 107 are arranged in parallel.
At intersections between each electrode 107 and each gate electrode 109 are bored openings 110, in which conical field emission type cathodes K are formed on the cathodes 107, respectively.
This field emission type cathode K is made of such materials that electron emission occurs due to the tunnel effect by impressing the electric field, e.g. on the level of 106 to 107 [v/cm] on molybdenum, tungsten, chromium and so on.
For better understanding the construction of cathode structure including the field emission type cathode K and the gate electrode, etc. forming the prior art plane type display device will be described together with an example of its manufacturing process in reference to manufacturing process diagrams of FIG. 2 to FIG. 5.
First of all, as described with FIG. 1, the cathode electrodes 107 are formed on the inner surface of the rear panel 105 along one direction, e.g. the vertical scanning direction.
These cathode electrodes 107 are formed into a predetermined pattern, e.g. by evaporating or sputtering a metal layer of chromium, etc. entirely And then etching it selectively by photolithography.
Next, as shown in FIG. 2, this patterned cathode electrodes 107 are coated entirely with the insulation layer 108 by sputtering, etc. and further on this layer a metal layer 111 becoming finally the gate electrodes 109 is formed, e.g. by evaporating or sputtering the metals of high melting point such as molybdenum, tungsten, etc.
As shown in FIG. 3 though not shown, a resist pattern by the photoresist, etc. is formed and using this as a mask the anisotropic etching, e.g. RIE (reactive ion-beam etching) is carried out on the metal layer 111 to form into the predetermined pattern, namely, to form the beltlike gate electrode 109 extending in the horizontal direction perpendicular to the extension of the cathode electrode 107 shown in FIG. 1. At the same time, at the intersections between the gate electrodes 109 and the cathode electrodes 107, for example, a plurality of small holes 111h are bored, respectively.
Next, though these small holes 111h, for example, a chemical etching which exhibits no etching property to the gate electrode 109, i.e. the metal layer 111 but exhibits the isotropic etching property to the insulation layer 108 is carried out to form cavities 112 having an opening width greater than that of the small holes 111h with a depth over a whole thickness of the insulation layer 108.
In this way, as shown in FIG. 1, at the intersections between the cathode electrodes 107 and the gate electrodes 109 are formed the openings 110 including the cavities 112 and the small holes 111h. 
Next, as shown in FIG. 4, the gate electrode 109 is covered with a metal layer 113 made of e.g. aluminum, nickel, and so forth by an oblique evaporation. This oblique evaporation is carried out while the rear panel 105 is rotated in its plane to form round holes 114 having a conical inner circumference around the small holes 111h. 
In this case, the evaporation of metal layer 113 is carried out at such a selected angle that the inside of cavities 112 may not be coated through the small holes 111h. 
Subsequently, a field emission type cathode material, namely, a metal having a high melting point and a low work function such as tungsten, molybdenum, etc. is adhered through the round holes 114 on the cathode electrode 107 inside the cavities 112 at right angles to this cathode electrode surface by evaporation, sputtering and so on. In this case, although the evaporation is carried out at right angles, because that cathode material forms such a slant face that follows a slant face of the metal layer 113 around the round holes 114, when reaching some thickness, the round holes 114 turn into blocked conditions. Consequently, conical dotlike cathodes K each of which has a triangular section are formed on the cathode electrode 107 within each cavity 112.
Thereafter, as shown in FIG. 5, the metal layer 113 and the cathode material formed thereon shown in FIG. 4 are removed, thereby causing the conical dotlike cathodes K each having a triangular section to be formed inside the opening 110 on the beltform, or stripeform cathode electrodes 107.
The cathodes K are surrounded by the insulation layer 108 and therefore insulated electrically from the cathode electrode 107. In opposition to each cathode K are arranged the gate electrodes 109 through which the aforesaid small holes 111h are bored as an electron passing holes. In this way, the cathode structure is constructed.
The cathode structure in which the field emission type cathode K is thus formed on the cathode electrode 107 and the gate electrode 109 is further formed above and across the cathode K is arranged in opposition to the white colour screen 101.
In the thus constructed display device body 102, the fluorescent screen 101, i.e. the metal-backed layer 106 is given a high anode voltage being positive to the cathode and also, for example, between the cathode electrode 107 and the gate electrode 109 is impressed a voltage which enables electrons to be emitted sequentially from the field emission type cathode at their intersection. For example, a voltage of 100 v relative to the cathode electrode 107 impressed on the gate electrode 109 is modulated in sequence according to display contents in order to direct the resulting electron beam from the tip of cathode K towards the white colour fluorescent screen 101.
In this way, a white colour image of light emitting pattern corresponding to each colour can be obtained in the time division manner by the display device body 102, and at the same time the colour shutter 103 is switched in synchronism with that time division display to derive a light corresponding to each colour.
Thus, optical images of red, green and blue are derived in sequence to display a colour picture as a whole.
As described above, in the plane type display device 100 having the conventional structure shown in FIG. 1, the field emission type cathode K opposing to the fluorescent screen is formed into a cone whose section is a triangular form due to the manufacturing process described referring to FIG. 2 to FIG. 5, thus causing the electric field to concentrate on the tip of the cone for raising the electron emission.
However, with the development of high technology of today, it is desired to make more efficiently sharp the electron emitting portion of the field emission type cathode K forming this plane type display device.
Moreover, when the cathode K is formed as described referring to FIGS. 2 to 5, its tip will have a shape whose radius of curvature is relatively gradual to the extent that the radius of curvature at the tip is dozens of nm, e.g. about sixty nm. In order to aim at the latest high resolution, it is needed to form this further finely for efficient electric field concentration and electron emission.
Thus, the present inventors et al have repeated studying devotedly and, as a result, come to provide a field emission type cathode, an electron emitting apparatus and a process for manufacturing the electron emitting apparatus in which the field emission type cathode K forming the plane type display device is made finer and sharper to enable further efficient concentration of electric field.
The field emission type cathode according to the present invention has a multilayered structure in which conductive platelike particles are piled.
The electron emitting apparatus according to the present invention is such that the field emission type cathodes are arranged in opposition to the fluorescent screen and each of the cathodes has a multilayered structure in which the conductive platelike particles are piled. By applying a predetermined electric field to the cathode, electrons will be emitted from its end surface.
The process for manufacturing the electron emitting apparatus according to the present invention has steps of forming a pile of layers of conductive platelike particles made into the multilayered structure by piling the conductive platelike particles on the field emission type cathode forming surface constituting the electron emitting apparatus, and forming an edge portion for concentrating the electric field on the end surface of layered pile of platelike particles by pattern-etching the layered pile of platelike particles.
That is, according to the present invention, because the field emission type cathode K is made up of the layered pile of platelike particles, the electron emitting portion of the cathode K is made finer and sharper, thereby causing the efficient concentration of electric field and enhancing the efficiency of electron emission.